The present invention relates to a reflective prism device for receiving a light beam emitted from a device such as a survey instrument and for reflecting it toward the survey instrument. The invention relates, in particular, to a reflective prism device with a function to perform optical communications, in which communication data is synthesized in the light beam from the survey instrument.
In a survey instrument, in particular, in a theodolite, there has been a trend in recent years that the system for reading angle measurement data has been changed from an optical reading system to an electrical reading system. Further, an electronic survey instrument incorporated with light wave distance measuring function is now the main stream in this field. In such new type of survey instruments, a light beam for measurement, i.e. range-finding light, is projected to a prism device, which is a target object, and distance is measured according to the range-finding light reflected from the prism device. Some of the survey instruments for light wave distance measurement used in recent years are provided with an optical communication device in which data for communication is synthesized with the range-finding light to be projected, and various types of information such as data for working instructions, measurement result, etc. are transmitted to a reflective prism device from the survey instrument.
FIG. 10 represents the electronic survey instrument as described above and a reflective prism device provided with a reflective prism, and it shows how survey operation is performed to determine a setting point.
In this figure, reference numeral 1 represents an electronic survey instrument installed at a known point, and a reflective prism device 2 for the survey instrument 1 is erected at a setting point. The electronic survey instrument 1 is incorporated with means for electrically reading angle measurement data and also with light wave survey means for surveying operation using light wave of range-finding light. Also, the reflective prism device 2 comprises a prism unit 3 and a data communication unit 4, which reflect a range-finding light 5 toward the survey instrument 1.
From the survey instrument 1, the reflective prism device 2 is collimated, and angle measurement and distance measurement are performed. The range-finding light 5 emitted from the survey instrument 1 is reflected by the prism unit 3 of the reflective prism device 2. The survey instrument 1 receives the reflected range-finding light, and the distance is measured. Distance measurement is performed by several tens of times in a second, for example, and the mean value is calculated as the measured value. If the measured value is different from the desired setting value, an instruction to change position is transmitted to an operator who is positioned on the side of the reflective prism device 2.
The instruction to change position is given via the range-finding light 5. Survey data such as measured distance, measured angle, etc. obtained at the survey instrument 1 or data relating to the setting position based on the survey data, e.g. information on the instruction to change position such as moving in rightward direction, for example, is synthesized in the range-finding light 5 by modulating the range-finding light 5. The range-finding light 5 is transmitted to the reflective prism device 2 as a light beam, which also serves as communication light.
The data communication unit 4 receives the range-finding light 5, and the information synthesized in the range-finding light 5 is separated and displayed. Or, communication is transmitted from the data communication unit 4 to the survey instrument 1 when necessary.
FIG. 11 shows a schematic optical arrangement of the survey instrument 1 and the reflective prism device 2. Brief description will be given now on an optical system comprising the survey instrument 1 and the reflective prism device 2.
The optical system for irradiating and receiving the range-finding light comprises a light source 10 for emitting the range-finding light 5, an irradiating optical system for irradiating the range-finding light 5 from the light source 10 to the reflective prism device 2, a photodetection optical system for guiding the reflection light from the reflective prism device 2, and a photodetection element 13 for receiving the reflection light guided by the photodetection optical system.
The range-finding light 5 from the light source 10 is reflected by a reflection mirror 11 and is directed toward an objective lens 12, which serves as the irradiating optical system. After being turned to approximately parallel beams by the objective lens 12, the range-finding light 5 is projected toward the prism unit 3 of the reflective prism device 2, and it is reflected by the prism unit 3. The reflected range-finding light 5' is directed again toward the objective lens 12. As shown in the figure, the prism unit 3 of the reflective prism device 2 comprises a corner cube, which serves as a retroreflective prism, and a reflection sheet, etc.
After passing through the objective lens 12, the reflected range-finding light 5' is focused by the objective lens 12, and it is deviated from the optical axis of the light source 10 as it is reflected by the reflection mirror 11, and an image is formed on the photodetection element 13.
As it is evident from FIG. 10, in the reflective prism device 2, the prism unit 3 and the data communication unit 4 are aligned in parallel in left-to-right direction or updown direction. In particular, when the data communication unit 4 is mounted after the prism unit, it is arranged in parallel to the prism unit.
The range-finding light 5 is irradiated as the approximately parallel light beams, and the use of parallel beams makes it possible to measure long distance. As described above, the prism unit 3 and the data communication unit 4 are arranged in parallel, and these cannot be disposed on the same optical axis. In general, the range-finding light is irradiated as parallel beams. Because the reflective prism device 2 is installed at long distance, the beams are spread over a certain angle although the beams are called "parallel beams". The spreading of light beams or luminous fluxes covers the prism unit and the data communication unit which are arranged in parallel, and the range-finding light 5 is projected to the prism unit and the data communication unit.
However, there is almost no spreading of luminous fluxes in case of near distance survey operation, and a problem arises in that the range-finding light 5 cannot cover the data communication unit, which is arranged in parallel to the prism unit when the prism unit is collimated. This leads to the situation that information cannot be transmitted via optical communications in case of near distance survey operation.